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600ohm to 50ohm balun or transformer?

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btm
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600ohm to 50ohm balun or transformer?

Postby btm » Fri Aug 31, 2012 5:31 am

I've purchased a Motorola R1150B Code Synthesizer for testing Minitor pagers. The manual says the two test jacks (banana plugs) are 600ohm balanced output. Most signal generators seem to have a 50ohm BNC external modulation input. What's the best way to convert this audio signal? Searching for a balun tends to lead to large units designed for high power transmission antennas. Is a small transformer appropriate? How about Mouser # 546-101R (Hammond 101R)? Please inform me if I'm horribly wrong.

http://www.mouser.com/ProductDetail/Hammond/101R/?qs=d90v4oKdVx2RPpzHKzVr6Q%3d%3d

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Re: 600ohm to 50ohm balun or transformer?

Postby DJP126 » Fri Aug 31, 2012 8:37 am

btm wrote:I've purchased a Motorola R1150B Code Synthesizer for testing Minitor pagers. The manual says the two test jacks (banana plugs) are 600ohm balanced output. Most signal generators seem to have a 50ohm BNC external modulation input. What's the best way to convert this audio signal? Searching for a balun tends to lead to large units designed for high power transmission antennas. Is a small transformer appropriate? How about Mouser # 546-101R (Hammond 101R)? Please inform me if I'm horribly wrong.

http://www.mouser.com/ProductDetail/Hammond/101R/?qs=d90v4oKdVx2RPpzHKzVr6Q%3d%3d


Motorola used to sell one for the R1150 but just because the external mod input on the generator is a BNC connector, it does NOT mean it's 50 ohms. Most of them are higher impedance.
Dave

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Re: 600ohm to 50ohm balun or transformer?

Postby Wowbagger » Fri Aug 31, 2012 8:40 am

Try looking for "audio transformer 600 ohm 50 ohm bnc". The transformer doesn't care about balanced or unbalanced, it's how you connect the leads.
This is my opinion, not Aeroflex's.

I WILL NOT give you proprietary information. I make too much money to jeopardize my job.

I AM NOT the Service department: You want official info, manuals, service info, parts, calibration, etc., contact Aeroflex directly, please.

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Re: 600ohm to 50ohm balun or transformer?

Postby jry » Fri Aug 31, 2012 11:25 am

used those for years and never really gave much thought to exactly matching the impedance since really all you are looking for is the correct deviation level and minimal distortion. The output level adjust will compensate for any differences in the impedance between the two devices.

Bottom line is I would not worry about it going into a signal generator or service monitor. just get a banana jack pair to BNC cable or adapter with a BNC jumper.

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Re: 600ohm to 50ohm balun or transformer?

Postby Wowbagger » Fri Aug 31, 2012 1:41 pm

Careful: there are devices where the audio HAS to be balanced - grounding one side will cause issues from hum to smoke leakage.

Just using a banana to BNC won't make it balanced.
This is my opinion, not Aeroflex's.

I WILL NOT give you proprietary information. I make too much money to jeopardize my job.

I AM NOT the Service department: You want official info, manuals, service info, parts, calibration, etc., contact Aeroflex directly, please.

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Bill_G
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Re: 600ohm to 50ohm balun or transformer?

Postby Bill_G » Fri Aug 31, 2012 2:02 pm

This will work - a CATV balun BNC to screw terminal.

Image

http://www.mcmelectronics.com/product/D ... 0-/50-7750

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Re: 600ohm to 50ohm balun or transformer?

Postby jry » Sat Sep 01, 2012 5:55 am

The R11XX analog output is balanced ( essentially audio transformer secondary) which really does not care which side you ground or not.

Part of the reason for this is the tone remote functionality for testing base stations over long analog lines where the need for 600 ohm balanced output is really needed.

Running into your typical service monitor or signal generator within a few feet with just a straight through cable is fine.

Have run these into a number of service monitors and generators with zero issues using the analog output this way.

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Re: 600ohm to 50ohm balun or transformer?

Postby Will » Thu Sep 06, 2012 10:00 am

Bill_G wrote:This will work - a CATV balun BNC to screw terminal.

Image

http://www.mcmelectronics.com/product/D ... 0-/50-7750



NO

That is for low level RF, we are talking audio...

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Re: 600ohm to 50ohm balun or transformer?

Postby Bill_G » Thu Sep 06, 2012 4:41 pm

I know. It will work (with some attenuation of course). They are pretty general purpose.

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Re: 600ohm to 50ohm balun or transformer?

Postby Will » Sat Sep 08, 2012 5:34 pm

Bill_G wrote:I know. It will work (with some attenuation of course). They are pretty general purpose.


No, the balun will not pas any audio. Even at RF the low end is above 20 mHz.

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Bill_G
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Re: 600ohm to 50ohm balun or transformer?

Postby Bill_G » Sat Sep 08, 2012 7:52 pm

Will wrote:
Bill_G wrote:I know. It will work (with some attenuation of course). They are pretty general purpose.


No, the balun will not pas any audio. Even at RF the low end is above 20 mHz.


Understood. Theoretically you should be correct, and yet they do pass audio. I've used them before. They are a convenient form factor, and I've used them to couple an external simulcast PL gen with a BNC connector into a Quantar on through the 25pr connector.

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Re: 600ohm to 50ohm balun or transformer?

Postby Al » Sat Sep 08, 2012 8:20 pm

Baluns do not have the property of DC isolation between input and output, so if you don't mind grounding one side of the test unit's audio output for DC and it doesn't destroy the audio output amp in the radio...transformer isolation is the best way, and 1:1 audio transformers are as inexpensive as a balun from suppliers like Mouser. I keep an old REP-111C telephone repeat coil(transformer) around for just such uses. It'll match 600 to 150 or 50 ohm circuits while providing DC isolation


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